Fiber-optic communication networks serve a key demand of the information age by providing high-speed data between network nodes. Fiber optic communication networks include an aggregation of interconnected fiber-optic links. Simply stated, a fiber-optic link involves an optical signal source that emits information in the form of light into an optical fiber. Due to principles of internal reflection, the optical signal propagates through the optical fiber until it is eventually received into an optical signal receiver. If the fiber-optic link is bi-directional, information may be optically communicated in reverse typically using a separate optical fiber.
Fiber-optic links are used in a wide variety of applications, each requiring different lengths of fiber-optic links. For instance, relatively short fiber-optic links may be used to communicate information between a computer and its proximate peripherals, or between local video source (such as a DVD or DVR) and a television. On the opposite extreme, however, fiber-optic links may extend hundreds or even thousands of kilometers when the information is to be communicated between two network nodes.
Long-haul and ultra-long-haul optics refers to the transmission of light signals over long fiber-optic links on the order of hundreds or thousands of kilometers. Transmission of optic signals over such long distances presents enormous technical challenges. Significant time and resources may be required for any improvement in the art of long-haul and ultra-long-haul optical communication. Each improvement can represent a significant advance since such improvements often lead to the more widespread availability of communication throughout the globe. Thus, such advances may potentially accelerate humankind's ability to collaborate, learn, do business, and the like, regardless of where an individual resides on the globe. Indeed, long-haul and ultra-long-haul fiber optic technology provides the communication infrastructure backbone upon which the global economy may more easily thrive.
One of the many challenges that developers of long-haul optic links face involves reliability. The long reach and large carrying capacity of long-haul fiber optic links makes such links heavily relied upon as a functioning component of the Internet, or as a vehicle for communicating voice information. A competing challenge is electrical power consumption. In long-haul optic links, power may not be necessarily available at points in the link (such as repeaters) that might require electrical power. This is especially true in the case of a submarine repeater that is situated on an ocean floor. Accordingly, power is often delivered to such points using an electrical conductor that is integrated with, or is associated with the optical cable. Since large distances are involved, much of the electrical power is lost as heat throughout the length of the electrical conductor.
In addition, the spacing of repeaters in a submarine link affects the optical quality of the transmitted signals, the electrical power consumption, and the cost of the link. In general, an increase in repeater spacing decreases the electrical power consumption and the link cost which is desirable, but also decreases the signal quality which is undesirable. Accordingly, repeater designs which improve the signal quality at greater repeater spacing and improve the electrical efficiency provide significant improvements to the art of long-haul and ultra-long-haul optics technology.
Prior approaches have increased the repeater spacing by using a discrete Erbium-doped fiber amplifier (EDFA) within the repeater in combination with 1) distributed backward Raman amplification, 2) distributed backward Raman amplification which additionally pumps a remote discrete EDFA, or 3) a remote discrete EDFA without Raman amplification.